1. Field of the Invention
The present invention relates to a radar system which detects neighboring objects, and to a vehicle controller installed in a vehicle, which includes such a radar system, and which performs driving control of the vehicle.
Priority is claimed on Japanese Patent Application No. 2004-203302, the content of which is incorporated herein by reference.
2. Description of Related Art
In the past, in a radar system for a vehicle which detects objects in the vicinity of the vehicle and which includes within its detection range the surface of the road upon which the vehicle is running, there have been included a signal transmission section which emits an electromagnetic wave which is frequency modulated, a signal receiving section which receives electromagnetic wave that is reflected from objects and obtains beat signals by mixing this received wave with a part of the electromagnetic wave, and a signal processing section which detects objects in the vicinity of the vehicle by analyzing the frequency of the beat signal. In the signal processing section of such a device, the first threshold which takes the frequency of the beat signal as a parameter of the signal receiving level, and the second threshold which is higher than the first threshold value, are set. The signal processing section, along with using the beat frequency which exceeds the second threshold for detection of objects in the vicinity, makes the decision that dirt is present upon the signal transmission section or the signal receiving section, if the number of occurrences of a beat frequency of a received signal level which exceeds the first threshold in a predetermined frequency range, is less than a predetermined value within a predetermined time period.
Hence, since the received signal level of the signal which is reflected by the road surface and which returns to the signal receiving section, is lower than the average received signal level of the signal which is reflected by objects that are actually required to be detected such as a vehicle ahead of the subject vehicle or an obstruction or the like, by setting the second threshold to be higher than the received signal level of the signal which is reflected from the road surface and which is the noise, is eliminated during object detection and accordingly it becomes possible to perform accurate detection. Furthermore, by setting the first threshold to be lower than the average received signal level of the signal which is reflected from the road surface, it becomes possible for a signal of receiving level which exceeds the first threshold to be always received while the vehicle is running. In other words, if a beat frequency of a level which exceeds the first threshold merely appears within a predetermined period of time, it may be decided that the received signal level has become lower due to dirt (for example, refer to Japanese Patent Publication No. 3428009).
However if an attempt is made to utilize, as a receiving antenna for such a prior art type radar system, an antenna array which includes a plurality of receiving antennas and all of which have approximately the same signal receiving characteristics and directivity in the same direction, and which are arranged in a line with a predetermined gap between them, then the problem arises with such prior art devices that, in the event that dirt or the like has adhered to only a portion of the plurality of receiving antennas, it has not been possible to perform an accurate decision as to whether or not such dirt has adhered. In concrete terms since, for the receiving antennas to which no dirt has adhered, received signals whose level exceeds the first threshold continue to be received, accordingly, for the synthetic output signal of the antenna array, it is not possible to decide whether or not the received signal level has been deteriorated due to the presence of dirt, and even in the state in which, for example, dirt has actually adhered to one or more of the receiving antennas, it may be erroneously determined that the state is that in which no dirt has thus adhered, which is very undesirable. Accordingly, there is the problem in that it is not possible to determine in the device itself that, due to the adhesion of dirt upon a portion of the plurality of receiving antennas, the proper performance as an antenna array cannot be obtained.
The present invention has been conceived in the light of the above described problem, and it takes as its objective to provide a radar system which can decide simply and moreover accurately as to the presence of an external object adhered upon its antenna, and moreover to provide a vehicle controller which includes such a radar system, and which executes appropriate vehicle control based upon the presence of an external object adhered upon the antenna.